JPH02192014A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To provide electromagnetic conversion characteristics of a high level and traveling durability in combination by incorporating specific magnetic powder and polyurethane in which the negative functional group forms an intramolecular salt into a magnetic layer. CONSTITUTION:The magnetic powder which has >=35m<2>/g specific surface area in BET value, in which <=2.0wt.% silicon is incorporated and which has >=90 dyne/cm adsorption energy of water and the polyurethane in which the negative functional group forms the intramolecular salt are incorporated into the magnetic layer 2. Namely, the specific ratio of the silicon is incorporated into the magnetic powder of the highly fine particles having >=35m<2>/g BET value and the adsorption energy of water is made into >=90dyne/cm, by which both the electromagnetic conversion characteristics and the traveling durability are compatibly obtd. Further, the polyurethane in which the negative functional group forms the intramolecular salt is incorporated into the magnetic layer and, therefore, the dispersibility of the magnetic powder is improved. Both the electromagnetic conversion characteristics and the traveling durability are additionally improved in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to magnetic recording media such as magnetic tapes, magnetic sheets, and magnetic disks.

A conventional magnetic recording medium basically consists of a nonmagnetic support and a magnetic layer containing ferromagnetic powder, and is constructed by providing the magnetic layer on the nonmagnetic material.

Generally, the magnetic layer is formed by dispersing ferromagnetic powder in a binder.

In recent years, there has been a strong demand for high-density recording in magnetic recording media with such a configuration, especially magnetic recording media for VTRs, and magnetic recording media with higher performance, that is, with excellent electromagnetic conversion characteristics and running durability, have been strongly demanded. There is a need for magnetic recording media.

However, as magnetic powder becomes finer and finer, it becomes dramatically more difficult to disperse it in a binder. If the magnetic powder is insufficiently dispersed in the binder, the highly finely divided magnetic powder will not be able to fully demonstrate its original performance, resulting in poor electromagnetic conversion characteristics. In order to compensate for this poor electromagnetic conversion property, the surface of the magnetic layer is polished to a mirror finish in an insufficiently dispersed state to increase its smoothness. This not only increases the coefficient of friction, but also weakens the magnetic coating itself. In particular, it could not withstand repeated running under high temperature and high humidity conditions, causing phenomena such as edge damage, running stoppage, and magnetic layer peeling.

As described above, it has been extremely difficult to achieve both high-level electromagnetic conversion characteristics and running durability.

C.6 Purpose of the Invention An object of the present invention is to provide a magnetic recording medium that has both high-level electromagnetic conversion characteristics and running durability.

20 Structure of the invention and its effects The present invention relates to a magnetic recording medium in which a magnetic layer contains a certain magnetic powder and polyurethane in which a negative functional group forms an inner salt.

First, "polyurethane in which the negative group forms an inner salt" will be described.

First, the manufacturing method will be described.

Similar to the usual polyurethane synthesis method, it is synthesized by reacting a high molecular weight polyol (molecular weight 500 to 3000) such as a polycarbonate polyol, polyester polyol, polylactone polyol, or polyether polyol with a polyfunctional aromatic or aliphatic isocyanate. As a result, polyester polyurethane, polyether polyurethane, and polycarbonate polyurethane carbonated with phosgene or diphenyl carbonate are synthesized.

These polyurethanes are mainly polyisocyanate 1
also in the form of urethane resins or urethane prepolymers prepared by the reaction of ~ with polyols and optionally other copolymers and containing free isocyanate groups and/or hydroxyl groups or containing reactive end groups thereof (For example, urethane elastomer type ○) may be used. As the isocyanate component, various diisocyanate compounds such as hexamethylene diisocyanate (HMDI), diphenylmethane diisocyanate (MD I ), hydrogenated MDI (H, □M D I
) Toluene diisocyanate (TDI), 1.5 naphthalene diisocyanate (NDI), tolidine diisocyanate (TODI), lysine diisocyanate methyl ester (LDI), isophorone diisocyanate (IP)
DI) etc. can be used.

In addition, if necessary, 1,4-butanediol, 1゜6-
A low-molecular polyfunctional alcohol such as hexanediol or 1,3-butanediol is used to adjust the molecular weight, resin physical properties, etc.

The functional group forming the inner salt may be introduced into the isocyanate component, but it can also be introduced into the polyol component, and further into the above-mentioned low-molecular polyfunctional alcohol.

Polyester polyols in which the negative functional groups form an inner salt contain various dicarboxylic acid components, polyhydric alcohol components, and dicarboxylic acid components and/or negative functional groups in which the negative functional groups form an inner salt. It can be synthesized by polycondensing polyhydric alcohol components forming an inner salt.

Examples of dicarboxylic acid components include terephthalic acid, isophthalic acid, sebacic acid, adipic acid, trimerized lyluic acid, and maleic acid. As a polyhydric alcohol component,
Glycols such as ethylene glycol, propylene glycol, butylene glycol, and diethylene glycol, or polyhydric alcohols such as trimethylolpropane, hexanetriol, glycerin, trimethylolpropane, trimethylolethane, and pentaerythritol, or these glycols and polyhydric alcohols Two or more arbitrary types selected from these can be exemplified.

Polycarbonate polyols in which the negative functional group forms an inner salt are generally synthesized by a transesterification method between a polyhydric alcohol and a dialkyl carbonate or diallyl carbonate, or can be obtained by condensation of a polyhydric alcohol and phosgene. can.

When producing the above polyester polyol and polycarbonate polyol (including polycarbonate polyester polyol), the following aromatic polyhydric alcohols can be used. Moreover, when reacting the above-mentioned polyester polyol or polycarbonate polyol with polyisocyanate, the following aromatic polyhydric alcohol can be used.

Aromatic polyhydric alcohol: [n represents 1 or 2. ] [n-1,2] [R is -(C1,) z-1-CH(CH3)-CH
Indicates 2-CH2-.

X is -5O□-1-CO-1-C(CH3)2-1C
(CH+)z-Cu2-C(CHz)z- is shown. ] [
n represents 1 or 2. ] [n represents 1 or 2. ] [R represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, and R' represents a hydrogen atom, an alkyl group having 1 to 7 carbon atoms, or an aryl group. ] [n represents an integer of 1 to 10. ] In the polyurethane having these aromatic polyhydric alcohol components in the main chain, the content of these components is preferably 10 mo 1% or more of the entire polyhydric alcohol component.

In order to produce a lactone polyester polyol in which the negative functional group forms an inner salt, S-caprolactam, α-methyl-1-caprolactam, S-methyl-8-
The above functional group may be introduced into lactams such as caprolactam and γ-butyrolactam.

In order to produce a polyether polyol in which a negative functional group forms an inner salt, the above functional group may be introduced into ethylene oxide, propylene oxide, butylene oxide, or the like.

As the functional group forming the inner salt, a betaine group mentioned below can be exemplified.

A general method for synthesizing polyester is carried out by a condensation reaction between an acid component having an aliphatic or aromatic polyfunctional acid or a derivative thereof and an aliphatic or aromatic polyfunctional alcohol component. Intramolecular amphoteric base of the present invention (betaine group, etc.)
may be contained in either the acid component or the alcohol component, or a method of introducing a betaine group or the like into the polymer as a polymer reaction may be used. However, in consideration of unreacted components and the introduction rate, it is easier to control if the polymer monomer has the functional group.

Examples of the betaine group include a sulfobetaine group, a phosphobetaine group, and a carboxybetaine group. The general formula of these hequine type functional groups is expressed as follows.

Na (=Contained in the urethane chain.

x knee soi. -0-3o:l. -coo80 PO
3H00PO+.

-0PO□H2°A: Hydrogen or an alkyl group having 1 to 60 carbon atoms (eg, methyl group, ethyl group, etc.).

m: an integer from 1 to 10.

B Coo or C0NH0 R: an alkyl group, alkenyl group, or aryl group having 1 to 12 carbon atoms.

n, m: integers from 1 to 10.

Examples of usable betaine group-containing monomers include the compounds listed below, but it goes without saying that the polyurethane resin used in the present invention is not limited to those using these monomers.

The monomer in which the negative functional group forms an inner salt is available as a commercially available drug, but it can be easily obtained by the method described below.

1) Synthesis method using monochloroacetic acid RIN (CHz C00H)z +CI2. CH
z C0OHR = alkyl group such as methyl, ethyl, etc. 2) Synthesis method using monochlorosuccinic acid CH2-CO
OH 3) Synthesis method using propane sultone Synthesize a compound having a group, etc., react it with a polyfunctional isocyanate such as diisocyanate in equimolar amounts, and react with the NGO group on one side of the diisocyanate and the hydroxyl group in the above compound. get something Then, by reacting the OH groups of the polyurethane with the unreacted NGO groups, a polyurethane into which hetain groups and the like are introduced can be obtained.

Examples of the above-mentioned compounds having a hydroxyl group and a betaine group include, but are not limited to, the following compounds.

Furthermore, as a polymer reaction, a reaction for introducing betaine groups and the like into a polymer will be described. In this method, a compound having a hetain group or the like is reacted with an OH group present at the end or side chain of polyurethane whose chain has been extended to a predetermined molecular weight by a polymerization reaction. In this case, first, the amount of hydroxyl group and betaine CH2CH20H introduced into the polyurethane resin of the present invention is 0.01 to 1.0 mmo I! , / g, more preferably 0.1 to 0.5 mmo 17
g range. The amount of the above polar group introduced is 0.01 m
mo I! If it is less than ,/g, it will be difficult to see a sufficient effect on the dispersibility of the ferromagnetic powder. Furthermore, if the amount of the polar group introduced exceeds 1.0 mmoffi/g, intermolecular or intramolecular aggregation tends to occur, which not only adversely affects dispersibility but also causes selectivity to the solvent, making it difficult for ordinary general-purpose solvents to There is also a risk that it may become unusable.

Further, the number average molecular weight of the polyurethane resin according to the present invention is 5
000-100000, more preferably 10000-5
Preferably, it is in the range of 0000. If the number average molecular weight is less than 5,000, the coating film-forming ability of the resin is likely to be insufficient, and if the number average molecular weight exceeds 100,000, problems may occur in paint manufacturing processes such as mixing, transport, and coating. There is.

Synthesis Example (a) 1 mole of N-methyljetanolamine and 1 mole of propanesultone were reacted at a temperature of 120° C. for 3 hours to obtain a sulfobetaine type polyfunctional monomer.

Next, 1.5 moles of adipic acid, 1.7 moles of 1,4-butanediol, and 0.06 moles of the above sulfobetaine type acid-base polyfunctional monomer were charged, and the mixture was heated at 150 to 200°C for about 30 minutes.
The temperature was raised over time, and the reaction was further carried out at 200°C for 4 hours.
Unreacted raw materials were removed at ~5 mmHg, and the reaction continued until the acid value reached 2 or less. The molecular weight of the obtained copolymerized polyester is M
It was w2500. 165 g of copolymerized polyester was dissolved in 300 parts of methyl ethyl ketone, 80 parts of diphenylmethane diisocyanate was added, and the mixture was reacted for 2 hours at 80°C.
After reacting for an hour, 4 parts of 1,3-butanediol was added and the reaction was continued for 1 hour. The molecular weight of the obtained polyurethane is M w
= 35,000, Mn = 22,000.

The amount of "polyurethane whose negative group forms an inner salt" according to the present invention is preferably 100 to 1 part by weight, more preferably 50 to 2 parts by weight, per 100 parts by weight of the magnetic powder.

The magnetic recording medium of the present invention has the following remarkable features.

The present inventor focused on the properties of the surface of magnetic powder in the course of research to improve the dispersibility of magnetic powder and binder. especially,
It was necessary to know what kind of polarity the surface of the magnetic powder had and how the binder would bind to that polar part.

Here, the present inventor focused on "adsorption energy" and first applied this to a magnetic recording medium for the first time.

As a result of a more detailed study of "water adsorption energy," we determined that high-fine particle magnetic powder with a BET value of 35 nf/g or more contains a specific amount of silicon, and that the water adsorption energy is 90 dyne/cm or more. As a result, they succeeded in achieving both electromagnetic conversion characteristics and running durability. Furthermore, since the magnetic layer contains polyurethane in which negative functional groups form an inner salt, the dispersibility of the magnetic powder is dramatically improved compared to conventional polyurethane, and the electromagnetic conversion characteristics and running properties are improved. Both durability has been further improved.

That is, since highly fine particle magnetic powder with a BET value of 35 nf/g or more is particularly difficult to disperse, its surface activity is particularly important. In addition, since the magnetic powder contains 2.0% by weight or less of silicon, it is possible to impart appropriate activity to the surface of the magnetic powder, thereby improving the dispersibility of the magnetic powder.

Moreover, the water adsorption energy of the magnetic powder is 90dy.
It is important to specify ne/c+n or more, as this greatly improves the dispersibility of the magnetic powder in the binder.

Conversely, since the magnetic powder was made into highly fine particles as described above, the effect of setting the water adsorption energy to less than 90 dyne/cm was extremely large.

When we combined magnetic powder with high surface activity and polyurethane J, in which negative functional groups form an inner salt, we found that the electromagnetic conversion properties were higher than that of the conventional combination of magnetic powder and polyurethane. Both the running durability and the running durability have been dramatically improved.

The reason why good dispersibility can be obtained by specifying the adsorption energy between the magnetic powder and water as described above is thought to be as follows.

Regarding the influence of water in magnetic paints, first of all, water molecules are often preferentially adsorbed on the surface of a hydrophilic solid. The magnetic powder surface has large free energy and is stabilized by hydration. This adsorbed water cannot be removed by normal drying, and has a structure close to that of ice. If a binder (especially the above-mentioned polyurethane) is adsorbed on the surface of this microparticle, the binder will absorb the adsorbed water. interacts with the surface of the magnetic powder through the interface layer with a high dielectric constant. Therefore, by specifying the adsorption energy of water as described above, the binding force between the binder and the magnetic powder can be increased.

Regarding the effect of improving dispersibility by the polyurethane mentioned above,
It can be explained as follows.

The surface of magnetic powder such as metal oxide is complex, and the surface is charged with positive and negative charges due to surface hydroxyl groups due to hydration, structural defects, ion substitution, etc. Therefore, when selecting a binder for magnetic powder, consider the acidity, basicity, and
Basic strength, acidity, number of basic sites, etc. are important factors. For example, in order to uniformly disperse magnetic powder in a short time, it is necessary to use binders with acidic and basic (polar) groups of various strengths, and to adsorb these acidic and basic sites to the surface active sites of the magnetic powder. is ideal.

However, simply introducing functional groups of the same polarity into the binder was far from this ideal.

It is also conceivable to use a binder having a polar functional group and to simultaneously use binders having functional groups of the same polarity and different strengths. However, in this case, the magnetic powder is competitively adsorbed preferentially to the side of the binder having a stronger functional group, making it difficult to achieve sufficient adsorption as a whole, resulting in poor dispersion stability of the magnetic paint. Furthermore, it is also conceivable to use a binder having a polar functional group and to simultaneously use a binder having a different type of functional group. However, in this case, the interaction between the polar groups is strong, and adsorption of the binder to the surface of the magnetic powder is difficult to occur, and the viscosity of the magnetic paint increases, making it impossible to prepare a magnetic paint.

The present invention solves these problems, and since the acid sites and base sites in the inner salt in the binder are adsorbed to the surface active sites (base sites and acid sites) of the magnetic powder, the magnetic powder is It is thought that the adsorption power is high and the dispersibility is significantly improved.

Moreover, since the negative functional groups of the same binder form an inner salt, the above-mentioned problem does not occur.

In the present invention, in combination with the surface activity of the magnetic powder described above, -
It has significantly improved dispersibility.

The adsorption energy of water to magnetic powder is 95 dyne/
It is more preferable to set it to cm or more.

We will further discuss the adsorption energy of water to magnetic powder.

The adsorption energy of magnetic powder to water is calculated by the following formula.

Wa=γ8. . (1+cosθ) ・・・・・・・・・
・■Wa: Water adsorption energy θ: Contact angle of magnetic powder with water γ1. IL(,: 72.75 (dyne/cm)
A large value of Wa means that the force required to separate water from the magnetic powder is large, which means that the magnetic powder easily absorbs water and has a highly polar surface.

From the above formula, the contact angle θ of magnetic powder with water, cos θ
By finding , the adsorption energy of water can be calculated.

The penetration height of the medium that penetrates the sample powder layer using the countersunk principle! The relationship between time and time can be expressed by Washburn's equation.

t: Time (seconds) γL = Surface tension of liquid (dyne/cm) L: Viscosity of liquid (g/cm-sec) r: Capillary radius in powder layer (cm) θ: Contact angle penetration height l The relationship between the penetration weight WL is expressed by the following equation.

S 0 ε 6 ρL S; Measurement cross-sectional area (td) ρL = Liquid density (g/cnl) ε: - Empty pumping rate From ■ and ■, the relationship between the penetrating weight WL and the measurement time is expressed by the following equation:

A method is used in which water is directly infiltrated into the magnetic powder.

FIG. 1 is a partial sectional view schematically showing the measuring device.

First, 15 g of magnetic powder is weighed into a cylindrical cell 14.

This cell 14 is tapped 500 times with a tapping device at a rate of 40 times per minute. This results in a sample having a constant porosity.

For the sample thus prepared, the permeation speed of water into the magnetic powder is increased using a permeation rate measuring device ("Peneto Analyzer" manufactured by Hosokawa Micron) as shown in FIG.

An opening 14a is provided at the bottom of the cell 14, and the mesh 2
0 is attached, and a magnetic powder layer 18 exists on top of this with a filter paper 19 interposed therebetween. In this state, the cell 14 is hung on the hook 12 of the electronic balance 11, and the weight scale at this point is set to O. Put about half of the capacity of ion-exchanged water 15 into a deep Petri dish 16 with a depth of about 6 cm, place the Petri dish 16 on the lifter 17, raise the lifter 17, and mix the magnetic powder layer 18 and the ion-exchanged water 15. bring into contact.

From this point on 4. Changes in the weight of the cell 140 are measured, and the weight of the ion-exchanged water 15 permeating the magnetic powder layer 18 is input into the computer along the time axis. Once the ion-exchanged water 15 has sufficiently permeated the magnetic powder [1B], the weight will no longer change, so the measurement is terminated.

Here, the vertical axis is the square of the increased weight WL of the cell 14,
If time is plotted on the horizontal axis, the graph will be a straight line with a certain slope.

Specifically, t represents time, and K represents the slope of the straight line. ) From the graph, you can find the value of K by calculating the slope within a certain time.

From this and the above equation 0, here, S, ε・ρ,・r are known, and TL=72
．． 75 (dyne/cm), γt=1 (g
/c+n-5ec) to find cos θ. By substituting this value into the above equation 0, the adsorption energy between the magnetic powder and water can be determined.

In addition, in the above, "rBET value" refers to the surface area per unit weight, and is a physical quantity that is completely different from the average particle diameter. For example, even if the average particle diameter is the same, the specific surface area is large, Some have small specific surface areas.

To measure the specific surface area, for example, first heat the magnetic powder at 250°C.
The powder was degassed while being heat-treated for 30 to 60 minutes before and after to remove the adsorbed substances, and then introduced into a measuring device and the initial pressure of nitrogen was set at 0.5 kg/rrr. , Adsorption measurement is carried out using nitrogen at liquid nitrogen temperature (-195°C) (-Measurement method of specific surface area generally referred to as B, E, T method. For details, see J, Ame, Chen+, Soc.
, 60309 (193B)). This specific surface area (
As a measuring device for the BET value, it is possible to use the "powder measuring device (Canterthorpe)" jointly manufactured by Digestion Battery (1) and Digestion Ionics (2). A general explanation of the specific surface area and its measurement method can be found in "Measurement of Granules" (J.M., DiLLAVALLE, CLYDEO).
Co-authored by RRJr, Valve Pressure Journal; Published by Sangyo Toshosha).
Pages 170 to 1171, published by Nippon Kagaku Metals, Maruzen, April 30, 1960). is the same as the specific surface area in this specification).

The silicon content in the magnetic powder is 2.0% by weight or less, and more preferably 0.2 to 1.2% by weight. Even if the silicon content exceeds 2.0% by weight, the effect commensurate with the increase in silicon content may not be achieved, and the magnetic properties may deteriorate on the contrary. Here, "containing" includes the case where it is attached to the surface of the core.

The silicon can be attached to the magnetic powder by, for example, adding a soluble silicon compound to a dispersion prepared by dispersing the magnetic powder in an alkaline aqueous solution.

Examples of the silicon compound include orthosilicic acid (H4S
iO,), metasilicate (Hz S 1O3), metatrisilicate (H2S i20), metatrisilicate (H=S
is Ch), metatetrasilicic acid (H6S i40++
); - silicon oxide, silicon dioxide, sodium orthosilicate (Nans+o4), sodium metasilicate (NaSiO:+), barium metasilicate (K2SiO), calcium orthosilicate (C
a4SiO, ), calcium metasilicate (Ca2SiO,
3), barium metasilicate (Bag Sios),
Examples include metal silicate salts such as cobalt metasilicate (COz Si 03).

These silicon compounds may be used alone or in combination.
You may use a combination of more than one species.

Magnetic powder containing silicon can also be produced by bringing magnetic powder into contact with a gas containing silicon. In addition, in the case of metal magnetic powder obtained by thermal reduction of goethite,
The above-mentioned treatment of /l (and/or) Si may be performed at the production or treatment stage of the raw goethite and then reduced.

Preferably, aluminum and/or silicon are present in the surface region of the magnetic powder in the form of an oxide or a hydrous oxide.

Magnetic materials, especially ferromagnetic powders include 7FezO3, Co-containing 7Fez 03 , Fe3O4, Co-containing Fe5
0. Iron oxide magnetic powder such as: Fe, Ni, Co, Fe-A
E, Fe-Al-Ni, Fe-Al-Co.

Fe-Aj2-Ni-Co, Fe-Ni-Co alloy, F
e-Mn-Zn alloy, Fe-Ni-Zn alloy, Fe-C
o-Ni-Cr alloy, Fe-Co-N1-P alloy, Co
-Ni alloy, etc., Fe, Ni, C.

Metal magnetic powder mainly composed of: Various ferromagnetic powders such as CrO2 can be mentioned.

When the water content of the magnetic powder is increased beyond a certain level, the activity of the surface of the magnetic powder decreases, and the adsorption energy of water decreases. Therefore, the water content in the magnetic powder is 0.
It is preferably 3 to 1.0% by weight.

Next, the overall structure of the magnetic recording medium of the present invention will be further described.

Other known binders can also be used.

The binder that can be used in combination has an average molecular weight of about 10,000.
~200,000, such as urethane resin, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer,
Butadiene-acrylonitrile copolymer, polyamide resin, polyvinyl butyral, cellulose derivatives (cellulose acetate butyrate, cellulose diacetate, cellulose triacetate, cellulose propionate, nitrocellulose, etc.), styrene-butadiene copolymer, polyester resin, various Synthetic rubber, phenolic resin, epoxy resin, urea resin, melamine resin, phenoxy resin, silicone resin, acrylic reaction resin, mixture of high molecular weight polyester resin and isocyanate prepolymer, mixture of polyester polyol and polyisocyanate, urea formaldehyde resin, mixture of low molecular weight glycol/high molecular weight diol/isosiapho I.
and mixtures thereof.

These binders are -303M, -COOM, PO(0
M) Resin containing a hydrophilic polar group such as 2 (where M is hydrogen or an alkali metal such as lithium, potassium, or sodium; M is an alkali metal such as hydrogen, lithium, potassium, or sodium, or a hydrocarbon residue) It is good to be. That is,
These resins have polar groups in their molecules that improve their compatibility with the magnetic powder, which further improves the dispersibility of the magnetic powder and prevents agglomeration of the magnetic powder, thereby improving the stability of the coating liquid. This can also improve the durability of the medium.

The "polyurethane in which a negative functional group forms an inner salt" of the present invention is a vinyl chloride resin, a vinyl chloride copolymer (
It is preferable to use it in combination with vinyl chloride-vinyl acetate copolymer, etc.). In this case, the weight ratio of the polyurethane of the present invention to the vinyl chloride resin and vinyl chloride copolymer is (
The ratio is preferably from 2:8) to (8:2), and more preferably from (3-near) to (7:3). As the vinyl chloride copolymer, those containing the above-mentioned hydrophilic polar groups are particularly preferred.

The binder used in combination, especially the vinyl chloride copolymer, can be obtained by copolymerizing a vinyl chloride monomer, a copolymerizable monomer containing an alkali salt of sulfonic acid or phosphoric acid, and other copolymerizable monomers as necessary. Can be done.

Since this copolymer is based on vinyl synthesis, it is easy to synthesize, and various copolymer components can be selected, so that the properties of the copolymer can be optimally adjusted.

The metal of the above-mentioned sulfonic acid or phosphoric acid salt is an alkali metal (especially sodium, potassium, lithium), and potassium is particularly preferable in terms of solubility, reactivity, yield, etc.

The above copolymerizable monomer containing a sulfonate salt is CH2=CH3O, M CH2= CHCHz S 03 M CHz =C(CHi)CH□ SO:1MCH2=
CHCH20COCH(CH2C00R)03M CH2=CHCH20CL CH(OH)CH2303
M CHz =c (CH:l)COOC2H4SO3M
CHz = CHCOOC4Ha SO:l MCH
z =CHC0NHC(CH3)t cHz soi
can be mentioned.

In addition, as a phosphate, CHi =CHCH,0CH2CH(OH)CH20-
PO, MY+ CHz =CHC0NH-C(CH3)z CH2
-0-PO,MY” PO□ MXI CHz =CHCH20(CH2CHz o)mP
O, MX” In the above, M is an alkali metal, R is a carbon atom number of 1 to 2
0 alkyl groups, Yl is H, M or CH2=CH3O
,0CHz CH(OH)CH2-Y2 is H, M or CHz'=CHC0NHC(CHs)2 CHt-X
I is oH or OM, X ” 1. I CHz = CHCHg O (CH2CHz O)
m-1OH or OM. Also, n is 1 to 100. m is a positive number from 1 to 100.

Copolymerizable monomers to be copolymerized as necessary include known polymerizable monomers, such as various vinyl esters, vinylidene chloride, acrylonitrile, methacrylonitrile, styrene, acrylic acid, methacrylic acid, and various acrylic esters. , methacrylic ester, ethylene, propylene, isobutyne, pucdiene, isoprene, vinyl ether, aryl ether, aryl ester, acrylamide, methacrylamide, maleic acid, maleic ester and the like.

The binder is polymerized by a polymerization method such as emulsion polymerization, solution polymerization, suspension polymerization, or bulk polymerization. In either method, known techniques such as divisional addition or continuous addition of molecular weight regulators, polymerization initiators, and monomers can be applied as necessary.

The amount of monomer containing the salt of the acidic group in the binder is 0.0
It is preferably 1 to 30 mol%. If the amount of the salt-containing salt is too large, the solubility in solvents is poor and gelation is likely to occur. Moreover, if the amount of salt-containing upper salt is too small, desired properties cannot be obtained.

The vinyl chloride copolymer described above may further contain an epoxy group or a hydroxyl group. By the way, conventional vinyl chloride copolymers (for example, VAGH manufactured by U, C, C, Inc.) are composed of the following copolymer components.

fcH2-CH1T 0H: indicates a copolymerization unit.

However, it is thought that the CH3Co-0- group here does not easily contribute to the crosslinking reaction with the curing agent and the like. Therefore,
It is preferable to contain an epoxy group such as the following instead of CH3Co. For example, a copolymer having the following units may be mentioned.

H (χ: monomer unit portion containing an alkali metal salt of a sulfo group or a phospho group) Note that it is also possible to incorporate the above hetain type functional group into the vinyl chloride resin.

"Polyurecne in which negative functional groups form an inner salt"
may be used in combination with an epoxy resin (particularly a phenoxy resin), a polyester resin, or a nitrocellulose resin (hereinafter referred to as other resin).

In this case, the blending ratio of the urethane resin and other resin is 90 to 10 parts by weight, more preferably 8 parts by weight.
The amount is preferably 0 to 20 parts by weight. The above blending ratio is 90
If the amount exceeds 1 part by weight, the coating film becomes too brittle, the durability of the coating film is significantly deteriorated, and the adhesion to the support is also deteriorated. Further, if the above-mentioned blending ratio is less than 10 parts by weight, the magnetic powder tends to powder and fall off.

When a carbon blank is included in the magnetic layer, it is further advantageous in terms of improving runnability and electromagnetic conversion characteristics, the dispersibility is also improved to some extent, and the amount of residual solvent in the magnetic layer is further reduced.

If a light shielding carbon blank is used as such carbon black, the degree of light shielding can be further increased. As a light-shielding carbon blank35), for example, Raben 200 manufactured by Columbia Carbon Co., Ltd.
0 (specific surface area 190rrf/g, particle size 18m tt
), 2100.1170.1000, #100, #75, #40, #35, #30 manufactured by Mitsubishi Kasei ■ can be used.

Further, as the conductive carbon black, for example, Conductex (Columbia Carbon Co., Ltd.) is used.
x) 975 (BET value (hereinafter abbreviated as BET)
250 rrr/g, D B P oil absorption (hereinafter referred to as D
BP) 170mf/100gr, particle size 24mμ),
Conductenx 900 (BE T125 rr
r/g, particle size 27 mμ), Conductex 40-2
20 (particle size 20mAIm), Conductex S
C (B ET220 rK/gr, DB P115
mf/100gr, particle size 20mμ), Cabot Vulcan χC-72 (specific surface area 254rrf/g, particle size 30mμ), Palcan P
(BET143rrr/gr, DBP118
m 1 / 100 gr, particle size 20 mμ), Raven 1040.420, Black Pearls 2000 (particle size 15 mμ), #44 manufactured by Mitsubishi Kasei ■, etc.

Other carbon blacks that can be used in the present invention include Conductex (manufactured by Columbia Carbon) (
Conductex )-3C0(BET220rr(
/g, DBP115 mI! ,/100 g, particle size 2
0mμ), Vulcan manufactured by Cavont
9 (B E T140 rrf/g, D B P1
14 ml/100 g, particle size 19 mμ), 480 manufactured by Asahi Carbon Co., Ltd. (BE T117 rd/g, D
BP113 mj2/100 g, particle size 23 mμ), H3100 manufactured by Denki Kagaku Co., Ltd. (BET32 i/'g, DBP
180mj2/100g, particle size 53mμ), #22B manufactured by Mitsubishi Kasei (BET55rrr/g, DBP13
1 mff1/100 g, particle size 40 mμ), #2OB
(BET56rrr/g, DBP115 mff1/
100 g, particle size 40 m u), #3500 (B
ET47rrr/g, DB P2S5 mff1/
100 g, particle size 40 mμ), and in addition, CF9, #4000, MA-600 manufactured by Mitsubishi Kasei, and Black Pea manufactured by Cabot.
rls) L, Monarch (Monarck) 800
, Black Pearls 700, Black Pearls 1
000, Black Pearls 880, Black Pearls 900, Black Pearls 1300, Blank Pearls 2000, Sterling ■
, Raven manufactured by Columbia Carbon Co.
) 4101 Raben 3200, Raben 430, Raben 450, Raben 825, Raben 1255, Raben 1035, Raben 1000, Raben 5000
, Ketchen Black FC, etc.

Furthermore, in the present invention, durability can be improved by further adding a polyisocyanate curing agent to the magnetic paint containing a binder.

Examples of such polyisocyanate curing agents include bifunctional isocyanates such as tolylene diisocyanate, diphenylmethane diisocyanate, and hexane diisocyanate, as well as coronate and Nippon Polyurethane Industries.
Trifunctional isocyanates such as Desmodul (manufactured by Bayer AG), desmodulite (manufactured by Bayer AG), or urethane prepolymers containing isocyanate groups at both ends, which are conventionally used as curing agents, can also be used as curing agents. Any polyisocyanate can be used. The polyisocyanate curing agent is used in an amount of 5 to 80 parts by weight based on the total amount of binder.

The magnetic recording medium of the present invention has, for example, as shown in FIG.
It has a magnetic layer 2 on a non-magnetic support 1 such as polyethylene terephthalate, and if necessary, a BCC 50 is provided on the opposite side of the magnetic layer 2. Also,
As shown in FIG. 3, an overcoat layer (QC layer) 4 may be provided on the magnetic layer 2 of the magnetic recording medium shown in FIG.

Further, the magnetic recording media shown in FIGS. 2 and 3 may have an undercoat layer (not disclosed) provided between the magnetic layer 2 and the support 1, or may have an undercoat layer provided between the magnetic layer 2 and the support 1. You don't have to. The support may also be subjected to corona discharge treatment.

The magnetic layer 2 can contain a fatty acid and/or a fatty acid ester as a lubricant.

As a result, it is possible to enhance each of the features of the two while canceling out the defects that occur when used alone, improving the lubrication effect, and increasing still image durability, running stability, S/N ratio, etc. In this case, the amount of fatty acid added is preferably 0.2 to 10 parts by weight per 100 parts by weight of the magnetic powder.
Even better is 0 parts by weight. If the fatty acid content falls outside of this range, the dispersibility of the magnetic powder decreases, and the runnability of the medium tends to decrease, and if the fatty acid content exceeds this range, the fatty acid tends to seep out and output decreases. In addition, the amount of fatty acid ester added is preferably 0.1 to 10 parts by weight per 100 parts by weight of magnetic powder.
Even better is 0.2 to 8.5 parts by weight. If the amount of ester is outside this range and the amount of ester decreases, the effect of improving running performance will be poor, and if the amount increases, the ester will easily seep out and the output will decrease.

In addition, in order to better achieve the above effects, the weight ratio of fatty acids and fatty acid esters should be adjusted to -
10/90 to 90/10 is preferred. Note that fatty acids also have a dispersing effect, and it is thought that by using fatty acids, the amount of other low molecular weight dispersants used can be reduced, and the Young's modulus of the magnetic recording medium can be improved by that amount.

Fatty acids may be monobasic or dibasic.

Fatty acids having 6 to 30 carbon atoms, more preferably 12 to 22 carbon atoms, are preferred. Examples of fatty acids are as follows.

(1) Caproic acid (2) Caprylic acid (3) Capric acid (4) Lauric acid (5) Myristic acid (6) Palmitic acid (7) Stearic acid (8) Isostearic acid (9) Rilunic acid (10) Linoleic acid (11) Oleic acid (12) Elaidic acid (13) Hehenic acid (14) Malonic acid (15) Succinic acid (16) Maleic acid (17) Glutaric acid (18) Adipic acid (19) Pimelic acid (20) Azelaic acid Acid (21) Sebacic acid (22) 1.12-Dodecanedicarboxylic acid (23) Octanedicarboxylic acid Examples of the above fatty acid esters are as follows.

(1) Oleyl oleate (2) Oleyl stearate (3) Isocetyl stearate (4) Dioleyl maleate (5) Butyl stearate (6) Butyl palmitate (7) Butyl myristate (8) Octyl myristate ( 9) Octyl palmitate (10) Amyl stearate (11) Amyl palmitate (12) Isobutyl oleate (13) Stearyl stearate (14) Lauryl oleate (15) Octyl oleate (16) Isobutyl oleate (17) Ethyl oleate (18) Isotridecyl oleate (19) 2-ethylhexyl stearate (20)
2-ethylhexyl myristate (21) ethyl stearate (22) 2-ethylhexyl palmitate (23) isopropyl palmitate (24) isopropyl myristate (25) butyl laurate (26) cetyl-2-ethyl hexalate ( 27) Dioleyl adipate (28) Diethyl adipate (29) Diisobutyl adipate (30) Diisodecyl adipate In addition to the above-mentioned fatty acids and fatty acid esters, other lubricants (such as silicone oil, carboxylic acid-modified, ester-modified Graphite, carbon fluoride, molybdenum disulfide, tungsten disulfide, fatty acid amide, α-olefin oxide, etc.) may be added to the magnetic layer.

Non-magnetic abrasive particles can also be added to the magnetic layer. For example, α-alumina, chromium oxide, titanium oxide, α-iron oxide, silicon oxide, silicon nitride, silicon carbide, zirconium oxide, zinc oxide, cerium oxide, magnesium oxide, boron nitride, etc. are used. The average particle diameter of this abrasive is preferably 0.6 μm or less. Moreover, it is preferable that the Mohs hardness is 5 or more.

In addition, the magnetic layer further contains an antistatic agent such as graphite.
A dispersing agent such as powdered lecithin or phosphate ester can be added. Furthermore, carbon black can also be used in combination.

In addition, the non-magnetic particles contained in the back coat layer are
It is more preferable that the average particle size is within the range of 10 mμ to 1000 mμ. This is because within the above range, the non-magnetic particles will not become too fine and the addition effect will be good.

Non-magnetic particles include silicon oxide, titanium oxide, aluminum oxide, chromium oxide, silicon carbide, calcium carbide,
Examples include zinc oxide, α-Fe, O, talc, kaolin, calcium sulfate, boron nitride, zinc fluoride, molybdenum dioxide, calcium carbide, barium sulfate, and the like. In addition, organic powders such as benzoguanamine resins, melamine resins, phthalocyanine pigments, etc. can also be used, and organic powders and the above-mentioned inorganic powders can also be used in combination.

Furthermore, it is more preferable to use carbon black together with the above-mentioned non-magnetic particles. This further stabilizes the running properties of the medium, and in combination with the effect of the non-magnetic particles described above, it is possible to further improve the durability of the medium.

The thickness of the magnetic layer is preferably thin in order to achieve a high S/N ratio, and thicker in terms of running performance and still durability. Therefore, the thickness is preferably 6.0 to 1.0 μm, and more preferably 5.0 to 2.0 μm. The surface roughness of the magnetic layer is an average surface roughness Ra of 0.005 to 0.
The thickness is preferably 0.020 μm. This does not reduce running performance and improves the S/N ratio.

Examples of materials for forming the non-magnetic support include polyesters such as polyethylene terephthalate and polyethylene 2,6-naphthalate; polyolefins such as polypropylene; cellulose derivatives such as cellulose triacetate and cellulose diacetate; plastics such as polycarbonate. etc. can be mentioned. Further C
u, A): It is also possible to use metals such as Zn, glass, and various ceramics such as so-called new ceramics (for example, boron nitride, silicon carbide, etc.).

The form of the non-magnetic support is not particularly limited, and may include tape,
It may be a sheet, card, disk, drum, etc., and various materials can be selected and used depending on the form and as necessary.

When the nonmagnetic support is in the form of a tape or sheet, the thickness is usually within the range of 3 to 100 μm, preferably within the range of 5 to 50 μm. Furthermore, in the case of a disk or card shape, the thickness can usually be within the range of 30 to 100 μm. Furthermore, in the case of a drum shape, it can be made into a cylindrical shape, etc., depending on the recorder used.

E, Example The present invention will be explained in detail below.

The components, proportions, order of operations, etc. shown below may be changed in various ways without departing from the spirit of the invention. In addition, in the following examples, all "parts" are parts by weight.

Preparation of Videotape First, a magnetic layer was formed on a 14 μm thick polyethylene terephthalate heath film as a support in the following manner.

That is, using the specified magnetic powder shown in Table 1 below, Table 1
A magnetic paint was prepared by dispersing each resin and various additives shown in the following. This magnetic paint was filtered through a 1 μm filter, 6 parts of trifunctional isocyanate (coronate) was added, and the mixture was spread on a support to a thickness of 4.0 μm. The mixture was coated and supercalendered to obtain magnetic layers having various compositions shown in Table 1.

Thereafter, a paint for the BC layer having the following composition was applied to the opposite surface of the magnetic layer to a dry thickness of 0.4 μm.

Carbon black (Conductex 975) 40
Part barium sulfate (average particle size 0.3 μm) 10 parts Nitrocellulose 25 parts N
-2301 (manufactured by Nippon Polyurethane) 25 parts Coronate 10 parts Cyclohexanone 400 parts Methyl ethyl ketone 250 parts Toluene
250 parts A wide magnetic film having a magnetic layer and a Bc layer of a predetermined thickness was obtained in this manner, and this was wound up.

This film was cut into 2-inch widths to produce the video tapes shown in Table 1. However, the numerical values shown in Table 1 represent parts by weight.

(Margin below) The magnetic powders shown in Table 1 are as follows.

Untreated CO-containing 7-FezO3 magnetic powder (C.

Containing M2.5 heavy contrast% 1 needle ratio 9) was suspended in an NaOH aqueous solution, a Na a Si04 aqueous solution was added to this, and while stirring well, carbon dioxide gas was blown into the suspension to neutralize it. Then, a film made of silicon oxide was formed on the surface of the magnetic powder. After washing this magnetic powder with water, it was dried at a predetermined drying temperature for a predetermined time.

The magnetic powders having the BET values shown in Table 1 were used in advance, and the concentration and amount of the Na4SiO4 aqueous solution were changed to obtain magnetic powders having the Si contents shown in Table 1. In addition, by changing the drying temperature and drying time of the magnetic powder after washing with water,
Each water content was set as shown in Table-1.

The adsorption energy to the magnetic powder was measured by the method described above. The water content of the magnetic powder was measured by the following method. That is, weigh the magnetic powder sample, and then weigh the magnetic powder sample.
Dry at 10°C for 21 hours, and immediately weigh the dried magnetic powder sample again.

Letting the weight loss of the magnetic powder sample be X, the water content (weight percentage) = (x/initial magnetic powder sample weight) xl
OO The vinyl chloride resins shown in Table-1 are as follows.

A: Vinyl chloride resin containing sulfo group Polar group concentration 0.03 mmo 42 / g Degree of polymerization 300 B: Vinyl chloride resin containing sulfo group and epoxy group Vinyl chloride component 77 wt% Sulfate group 0.8 cut t% Epoxy group 3. 9 wt% Hydroxyl group 0.5 slightly less than t% The polyurethanes shown in Table 1 are as follows.

Polyurethane (a) according to the present invention was synthesized as shown in Synthesis Example (a) above, and (b), (c), and (d) were synthesized in the same manner.

(a) Sulfobequin-type modified group content Number average molecular weight 22,000 7g -20'c Polar group concentration 0.04 mmoj! / gCH3 Small (b) carboxyhetaine type modification group content number average molecular weight 1
．． 50,000 Tg -10°C Polar group concentration 0.1 mmo
12/gH2 (c) Phosphobetaine type modification group content Number average molecular weight 30,000 Tg O°C polar group concentration 0
．． oR/g for 07 m H2 Clear CH2 Polyurethane chain (d) Contains sulfobetaine type modified group Weight average molecular weight 55,000 7g-5℃ Polar group concentration 0.05 Open 017°C Composition Nidiphenylmethane diisocyanate Bisphenol A-Propylene oxide ( (divalent) adduct isophthalic acid 1.4-butadiene adipic acid (mo-poor ratio) 3.2 1.1-3.6 1.6 7.5 CH3 ■ (CHz N CHz+ (CH2)3 Sulfo group-containing polyurethane : r U R-8300J (manufactured by Toyobo Co., Ltd.) <Evaluation of videotape performance> The characteristics shown in Table 2 below were evaluated for each videotape shown in Table 1.

The measurement method for each evaluation data is as follows.

Electromagnetic conversion characteristics Chroma output, Rf ratio output Lumi S/N: Measured using Vigtar HR-37000.

<Running, durability> Still life: NV-6200 (manufactured by Matsushita Electric) for 1
The time it takes for the RF low output to reach -2dB in still mode.

Edge damage: each videotape at 40°C 180%
The vehicle was run 100 times over its entire length under RH conditions. After this, the tape edge was observed over the entire length of the tape.

Shed: The condition of the head was observed when measuring "edge damage."

O...No stains.

△・・・・・・・・・Slight stains.

×・・・・・・There is dirt.

In addition, when measuring edge damage, we also measured bulge, coefficient of dynamic friction, and dropout.

Drone out: Use a dropout counter VD5M manufactured by Victor Japan Co., Ltd., and use a dropout counter VD5M made by Victor Company of Japan.
The output that decreased by dB or more was regarded as one dropout, and the total length was determined to be 1 qll, and the average value per minute was determined.

Surface resistivity measured with a two-surface electrometer.

(The following is a blank space) As shown in Table 2, the video tapes of the examples are excellent in both electromagnetic conversion characteristics and running durability.

Next, a videotape having the same configuration and prescription as the videotape of Example 1 was created. However, FIG. 4 shows how the Rf specific output changes when only the BET value of the magnetic powder is varied. Similarly, only the silicon adhesion amount of the magnetic powder was varied, and FIG. 5 shows how the R output changes accordingly.

Furthermore, by varying the water content in Example 1, the adsorption energy of water to the magnetic powder was varied, and FIG. 6 shows how the RE specific output changes in response to this variation.

In Example 1, the relationship between water content and water adsorption energy when the BET value and silicon content are fixed is shown.

From FIGS. 4 to 6, it is clear that the limitations based on the present invention are important (j7) I understand that it is important.

[Brief explanation of the drawing]

FIG. 1 is a partial sectional view schematically showing a permeation rate measuring device. FIGS. 2 and 3 are partially enlarged sectional views showing examples of magnetic recording media, respectively. FIG. 4 is a graph showing changes in Rf output with respect to changes in specific surface area of magnetic powder. Figure 5 shows Rf as a function of changes in the adhesion amount of silicon in magnetic powder.
It is a graph showing output changes. Figure 6 shows R for changes in adsorption energy of water to magnetic powder.
[This is a graph showing output changes. In addition, in the symbols shown in the drawings, 1......Nonmagnetic support 2...Magnetic layer 3-...Back coat layer (BC layer) )4・
......Overcoat layer (QC layer) 11...
......Electronic balance 14...Weighing cell 15...Ion exchange water 18...Magnetic powder layer .

Claims (1)

[Claims] 1. The specific surface area is 35 m^2/g or more in BET value,
A magnetic powder containing 2.0% by weight or less of silicon and having a water adsorption energy of 90 dyne/cm or more;
A magnetic recording medium in which a magnetic layer contains polyurethane in which negative functional groups form an inner salt.